Hydrofluorocarbons (HFCs) and in particular hydrofluoroolefins (HFOs), such as 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), are compounds known for their properties as coolants, heat-transfer fluids, extinguishers, propellants, foaming agents, swelling agents, gaseous dielectrics, polymerization medium or monomer, support fluids, agents for abrasives, drying agents and fluids for power production units. HFOs have been identified as desirable alternatives to HCFC on account of their low ODP (ozone depletion potential) and GWP (global warming potential) values.
Most of the processes for manufacturing hydrofluoroolefins involve a fluorination and/or dehydrohalogenation reaction. This type of reaction is performed in the gas phase and generates impurities which consequently need to be removed in order to obtain the desired compound in a sufficient degree of purity for the targeted applications.
For example, in the context of producing 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), the presence of impurities such as trans-1,3,3,3-tetrafluoro-1-propene (1234ze-E) is observed. Side products, for instance 1,1,1,2,2-pentafluoropropene, are also formed. Purification of this type of reaction mixture may be performed, for example, by distillation. However, when the compounds to be purified have boiling points that are too close or when they form azeotropic or quasi-azeotropic compositions, distillation is not an efficient process. Extractive distillation processes have thus been described.
WO 03/068716 discloses a process for recovering pentafluoroethane from a mixture comprising pentafluoroethane and chloropentafluoroethane by distillation in the presence of hexafluoropropene.
WO 98/19982 also discloses a process for purifying 1,1-difluoroethane by extractive distillation. The process consists in placing an extracting agent in contact with a mixture of 1,1-difluoroethane and vinyl chloride. The extracting agent is chosen from hydrocarbons, alcohols and chlorocarbons with a boiling point of between 10° C. and 120° C. As mentioned by WO 98/19982, the selection of the extracting agent may prove to be complex depending on the products to be separated.